Erika Sasaki of the Central Institute for Experimental Animals in Japan led a team in the creation of five marmosets with a gene from the jellyfish Aequorea victoria.

They are not the first glowing primates, but they are the first to demonstrate that the glowing gene “is maintained in the family—or germline,” the BBC added. In other words, the gene has “produced its protein in all the body tissues in a primate” and has been passed on to offspring, Science News reports.

The genetic trait—the marmosets glow green under UV light—is serving as an example of how gene modification could be used to study treatments of human diseases in animal subjects. Creating a transgenic line in primates has been attempted before.

Learn more about the study of genetics including DNA sequencing and genetic research with findingDulcinea’s Web Guide to Genetics.

The process involves injecting the gene in the animal via a “retrovirus.” Sasaki and her team “injected a virus, called lentivirus, into marmoset embryos,” Science News reports. “The virus carried the gene encoding an enhanced version of green fluorescent protein or GFP, which the virus inserts into the marmosets’ genome.”

Study coauthor Hideyuki Okano of the Keio University School of Medicine admitted that the innovation “may not be suitable for studying all diseases,” according to the BBC. But marmosets “can model human neurodegenerative diseases, especially those that are dominantly inherited—that is, diseases caused by mutation in a single copy of the gene,” Okano explained to Science News.

Marmosets are not as close to humans’ genetic makeup as other primates such as chimpanzees, but they are closer than mice, and the success of the Japanese team means “we will have a new animal model to work with,” Dr. Kieran Breen of the U.K.’s Parkinson's Disease Society told the Daily Mail.

Hailed as a possible source of “miracle cures” by Sky News and the “spark” of a “genetic engineering debate” by the Daily Mail, the glowing marmosets are causing a significant amount of concern. Their canine predecessor Ruppy, one of four fluorescent beagle puppies created by a South Korean team led by Byeong-Chun Lee, received less fanfare.

The Daily Mail explains that the research “raises the prospect of deliberately breeding monkey colonies with the genetic defects that cause incurable diseases.”

Dr. Breen of the Parkinson’s Disease Society believes the study is “potentially very exciting,” the Daily Mail reports. But Jarrod Bailey, a science consultant to the British Union for the Abolition of Vivisection (BUAV), told the BBC that the type of research conducted “does not have public support.”

Michelle Thew of BUAV went further than her colleague in the Daily Mail. “Instead of inflicting great suffering on other species, the research industry should be investing its substantial intellect, ingenuity and resources into finding more appropriate and humane methods to fight human diseases,” she said.

But “[d]isorders of higher brain function, such as Alzheimer's disease, are especially challenging to reproduce in rodents,” MIT’s Technology Review quoted Gerald Schatten and Shoukhrat Mitalipov as writing in the journal Nature, “and here, as with many other diseases, it is our closest animal relatives—the non-human primates—that offer potentially invaluable biological models.”